The present invention relates to a starting mechanism for an internal combustion engine having a diaphragm carburetor which has an intake channel that communicates with an intake port of the internal combustion engine, with the intake channel having a Venturi section. A butterfly valve is disposed in the intake channel and has a pivot range into which at least one fuel nozzle opens. A starter valve is disposed upstream of the Venturi section. For an additional air supply when the starter valve is closed, a by-pass conduit is provided, the rate of air flow of which is determined by a control element that is adjustable as a function of temperature.
A starting mechanism of this general type is known from EP-0 262 491 A 2. Formed in the housing of the diaphragm carburetor is an intake passage that is connected with the intake port of an internal combustion engine. Disposed in the intake passage, in the vicinity of a Venturi section, is a primary fuel nozzle, while in the pivot range of a butterfly valve that is disposed downstream of the Venturi section an idling nozzle opens. Upstream of the Venturi section is a starter valve, in which is formed a by-pass conduit for supplying air for combustion when the starter valve is closed. The by-pass conduit is controlled by a bimetal element that as a function of the ambient temperature in the intake passage of the diaphragm carburetor controls the rate of air flow in the by-pass conduit.
The starting of such gasoline-operated internal combustion engines, which are utilized as drive motors in manually guided implements such as power chainsaws, cut-off machines, brush cutters, blowers, or the like, requires the use of a rope pull, which is supposed to ensure a starting of the internal combustion engine after only a few pulls. It has been shown that with a position of the choke valve as designed, a starting of the internal combustion engine is ensured. However, when accelerating the engine at idling speed, an overly rich mixture can occur which in many cases can result in the engine dying. If a generally two-stroke or four-stroke engine has died due to the fuel mixture being too rich, it is often difficult for an inexperienced user to again start the engine up. With the known temperature-control regulation of the cross-sectional flow area of the by-pass conduit, although a metering of the air for combustion that is adapted to the temperature is ensured, the underpressure in the intake channel of the diaphragm carburetor also fluctuates with the alteration of the cross-sectional flow area of the by-pass conduit in the starter valve, which results in reactive effects upon the fuel supply.
It is therefore an object of the present invention to improve a starting mechanism of the aforementioned type for an internal combustion engine having a diaphragm carburetor in such a way that a reliable starting and continuous running of the internal combustion engine is ensured over a large temperature range without manual intervention from a user.